Methods for enhancing a wastewater treatment process

ABSTRACT

Methods for enhancing an activated sludge process including at least one biological reactor. A weighting agent impregnation subsystem is coupled to the biological reactor for mixing biological flocs and weighting agent to impregnate the weighting agent into the biological flocs to form weighted biological flocs. A weighting agent recovery subsystem is configured to recover the weighting agent from the weighted biological flocs and reintroducing the recovered weighting agent to the weighting agent impregnation subsystem.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 13/461,641 filed May 1, 2012, which is a continuation of U.S.application Ser. No. 12/584,545 filed on Sep. 8, 2009, which is acontinuation in part of U.S. application Ser. No. 12/008,216, filed Jan.9, 2008, which is now U.S. Pat. No. 7,695,623, which claims priority toU.S. Provisional Application No. 60/994,553, filed Sep. 20, 2007 andU.S. Provisional Application No. 60/879,373, filed Jan. 9, 2007, each ofwhich are incorporated by reference in their entirety for all purposes.

FIELD OF THE INVENTION

This invention relates to a system and method for enhancing a wastewatertreatment process.

BACKGROUND OF THE INVENTION

Municipal and industrial wastewater treatment facilities often includeprimary, secondary and tertiary processes to treat wastewater to removecontaminants, such as suspended solids, biodegradable organics,phosphorus, nitrogen, microbiological contaminants, and the like, toprovide a clean effluent. The clean effluent is typically subject tostrict local, state and federal regulations.

The primary treatment processes often includes screens, grit chambersand/or primary clarifiers to remove large solids and other suspendedmatter to provide a primary effluent. Activated sludge is one type ofsecondary process which utilizes a biological reactor(s) which containsa large population of microorganisms that ingest contaminants in theprimary effluent to form biological “flocs.” Oxygen is typically fedinto the biological reactor(s) to promote growth of these biologicalflocs. The combination of primary effluent, or in some cases raw sewage,and biological flocs, is commonly known as mixed liquor. The populationor concentration of microorganisms in the mixed liquor is often referredto as mixed liquor suspended solids (MLSS).

After sufficient treatment in the biological reactor, the biologicalflocs in the mixed liquor are then typically sent to a secondaryclarifier where the biological flocs are separated by gravity from themixed liquor to provide a secondary effluent and a settled sludge. Thesecondary effluent, or “clean” effluent, may be discharged back to theenvironment or processed by additional tertiary treatment processes. Themajority of the settled sludge in the secondary clarifier is typicallyrecycled back to the biological reactor by a return activated sludgesubsystem. The remaining, excess sludge is wasted from the system tocontrol the concentration of mixed liquor suspended solids.

However, separation of the biological flocs from the mixed liquor in thesecondary clarifier is difficult because the biological flocs are onlymarginally heavier than water, and therefore settle slowly. As a result,the secondary clarifier of a typical activated sludge process is oftenthe bottleneck in most wastewater treatment processes that utilizeactivated sludge as a secondary process. The crucial solids separationstep of the biological flocs from the mixed liquor in the secondaryclarifier is therefore typically the rate limiting process which isgoverned by a variety of factors, most notably the specific gravity, ordensity, of the biological flocs.

Moreover, solids separation in the secondary clarifier in a typicalactivated sludge processes may be unreliable due to the many types ofsettling problems that are caused by inter alia: overgrowth offilamentous organisms, viscous bulking caused by the overgrowth ofeither zoogleal organisms or exocellular polysaccharide material, pinfloc, straggler floc, excessive solids loading on the secondaryclarifiers, excessive secondary clarifier surface overflow rate, and thelike.

Sequencing batch reactor (SBR) systems may also be used to treatwastewater. A typical conventional SBR system includes one or moresequencing batch reactors which contains a large population ofmicroorganisms that ingest contaminants in the influent wastewater toform biological flocs and treat the wastewater. However, during thesettling phase of a typical conventional SBR system, the biologicalflocs settle slowly because they are only marginally heavier than water.The solids separation in the settling phase is also unreliable due tothe many types of settling problems discussed above. This can result inreduced treatment capacity and/or compromised effective quality.

Another method of treating wastewater, such as wastewater frombreweries, pharmaceutical plants, food processing plants, pulp and paperfacilities, ethanol production facilities, and the like, is to use ananaerobic treatment reactor. The anaerobic treatment reactor creates ananaerobic environment which contains a population of microorganisms thatingest contaminants in the influent wastewater to form biological flocsand treat the wastewater. The wastewater is typically fed near thebottom of the anaerobic treatment reactor and into a sludge blanketwhere the microorganisms consume the waste therein. In operation,wastewater fed into the bottom of the anaerobic treatment reactor flowsupward through the anaerobic sludge blanket to treat the wastewater.

However, if the flow rate of influent wastewater is too fast, theanaerobic sludge blanket can expand and become diffuse. The result maybe an excess loss of microorganisms in the treated effluent which maycompromise the quality of the treated effluent.

SUMMARY OF THE INVENTION

This invention features a system for enhancing an activated sludgeprocess including at least one biological reactor. A weighting agentimpregnation subsystem is coupled to the biological reactor for mixingbiological flocs and weighting agent to impregnate the weighting agentinto the biological flocs to form weighted biological flocs. A weightingagent recovery subsystem is configured to recover the weighting agentfrom the weighted biological flocs and reintroduce the recoveredweighting agent to the weighting agent impregnation subsystem.

In one embodiment, the weighting agent recovery subsystem may include aseparator subsystem for separating the weighting agent from the weightedbiological flocs. The separator subsystem may include a shear mill. Theseparator subsystem may include a centrifugal separator. The separatorsubsystem may include an ultrasonic separator. The separator subsystemmay include a shear mill and a wet drum magnetic separator. Theseparator subsystem may include a shear mill and a centrifugalseparator. The separator subsystem may include an ultrasonic separatorand a wet drum magnetic separator. The separator subsystem may includean ultrasonic separator and a centrifugal separator. The shear mill mayinclude rotor and a stator, wherein the rotor and/or the stator includeslots sized as to optimize separation of weighting agent from theweighted biological flocs. The weighting agent impregnation subsystemmay include a weighting agent storage tank and at least one line. Theweighting agent impregnation subsystem may include a weighting agentfeeder subsystem configured to control the delivery rate of theweighting agent from the weighting agent storage tank to the weightingagent impregnation tank. The weighting agent feeder subsystem mayinclude a pneumatic feeder subsystem. The pneumatic feeder subsystem mayinclude porous media disposed on selected areas of the inside of theweighting agent storage tank and the inside of the at least one line.The pneumatic feeder subsystem may be configured to deliver a controlledsupply of compressed air to the porous media to regulate fluidizationand delivery of the weighting agent to the weighting agent impregnationtank. The weighting agent impregnation subsystem may include animpregnation tank and at least one mixer. The weighting agentimpregnation subsystem may include a venturi mixer/eductor. The majorityof the weighting agent may have a particle size less than about 100 μm.The majority of the weighting agent may have a particle size less thanabout 40 μm. The majority of the weighting agent may have a particlesize less than about 20 μm. The weighting agent may include magnetite.The biological reactor may include at least one aeration tank and/or oneor more sequencing batch reactors for receiving a flow of wastewater andfor introducing dissolved oxygen to a population of microorganisms topromote growth of biological flocs in a mixed liquor defined by aconcentration of mixed liquor suspended solids. The at least onebiological reactor may be configured as at least one anaerobic treatmentreactor. The system may include a flocculant injection subsystemconfigured to introduce a flocculant to the mixed liquor to enhancesettling and thickening of weighted biological flocs and to provideagglomeration of non-impregnated biological flocs and/or partiallyimpregnated biological flocs with weighted biological flocs. The systemmay include at least one clarifier configured to collecting the weightedbiological flocs from the mixed liquor and configured to provide asecondary effluent and a settled sludge. The system may include a returnactivated sludge subsystem configured to recycle the majority of settledsludge to the biological reactor and/or to the weighting impregnationsubsystem. The system may further include a wasting subsystem configuredto waste remaining settled sludge of the weighting agent recoverysubsystem to control the population of the microorganisms in the mixedliquor. The capacity of the system may be increased by increasing theconcentration of mixed liquor suspended solids in the biological reactorby reducing the amount of the settled sludge wasted by the wastingsubsystem. The amount of settled sludge wasted by the wasting subsystemmay be reduced to increase the concentration of mixed liquor suspendedsolids for enhancing nitrification of ammonia in the mixed liquor. Thenitrification may be enhanced by increasing the amount of dissolvedoxygen introduced into the biological reactor. The biological reactormay include at least one anoxic zone configured to remove nitrogen fromthe mixed liquor. The biological reactor may include at least oneanaerobic zone configured to remove phosphorus from the settled sludge.The system may further include a coagulant addition subsystem for addingcoagulant to remove phosphorus by precipitation and/or coagulation. Thecoagulant addition subsystem may add to coagulant to the weighting agentimpregnation subsystem and/or the at least one biological reactor and/orthe flocculant injection subsystem to remove phosphorus by precipitationand/or coagulation. The weighting agent to a mixed liquor may be greaterthan about 1.5 to 1. The system secondary effluent may have a totalsuspended solids concentration less than about 30 mg/L. The weightingagent impregnation subsystem may be located downstream from thebiological reactor and before the secondary clarifier.

This invention also features a system for enhancing an activated sludgeprocess including at least one biological reactor. A weighting agentimpregnation subsystem coupled to the biological reactor for mixingbiological flocs and weighting agent having particle size less thanabout 100 μm to impregnate the weighting agent into the biological flocsto form weighted biological flocs. A weighting agent recovery subsystemis configured to recover the weighting agent from the weightedbiological flocs and reintroducing the recovered weighting agent to theweighting agent impregnation subsystem.

In one embodiment, the majority of the weighting agent may have aparticle size less than about 40 μm. The majority of the weighting agentmay have a particle size less than about 20 μm.

This invention also features a method for enhancing a wastewatertreatment process, the method including: a) receiving influentwastewater in at least one biological reactor, b) forming biologicalflocs in the biological reactor, c) impregnating weighting agent intothe biological flocs to form weighted biological flocs, and d)recovering weighting agent from the weighted biological flocs toreintroduce the weighting agent to step c).

In one embodiment, the method may include the step of separating theweighting agent from the weighted biological flocs. The method mayinclude the step of collecting the weighting agent and recycling theweighting agent to step c). The method may include the step of providingweighting agent in which the majority of the weighting agent has aparticle size less than about 100 μm. The method may include the step ofproviding weighting agent in which the majority of the weighting agenthas a particle size less than about 40 μm. The method may include thestep of providing weighting agent in which the majority of the weightingagent has a particle size less than about 20 μm. The method may includethe step of introducing dissolved oxygen to a population ofmicroorganisms to promote growth of biological flocs in a mixed liquordefined by a concentration of mixed liquor suspended solids. The methodmay further include the step of introducing a flocculant to the mixedliquor to enhance settling and thickening of the weighted biologicalflocs and to establish agglomeration of non-impregnated biological flocsand/or partially impregnated biological flocs with the weightedbiological flocs.

The subject invention, however, in other embodiments, need not achieveall these objectives and the claims hereof should not be limited tostructures or methods capable of achieving these objectives.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages will occur to those skilled inthe art from the following description of a preferred embodiment and theaccompanying drawings, in which:

FIG. 1 is a three-dimensional view of one embodiment of the system forenhancing a wastewater treatment process of this invention;

FIG. 2 is a schematic side view showing in further detail one embodimentof the weighting agent feeder subsystem shown in FIG. 1;

FIG. 3 is a microscopic photograph showing one example of weightingagent impregnated into a biological flocs to form a weighted biologicalflocs in accordance with this invention;

FIG. 4 is a schematic side-view showing another embodiment of theweighting agent impregnation subsystem shown in FIG. 1;

FIG. 5A is a schematic side-view of one embodiment of the separatorshown in FIG. 1;

FIG. 5B is a schematic top view showing one example of slots in therotor and stator of the shear mill shown in FIG. 5A;

FIG. 5C is a three-dimensional view of one embodiment of the shear millin FIG. 5A;

FIG. 6 is a three-dimensional front-view of another embodiment of theseparator shown in FIG. 1;

FIG. 7 is a three-dimensional front-view of yet another embodiment ofthe separator shown in FIG. 1;

FIG. 8 is a three-dimensional front-view of one example of a wet drummagnetic separator which may be utilized by the weighting agent recoverysubsystem shown in FIG. 1;

FIG. 9 is a three-dimensional view of another embodiment of the systemfor enhancing a wastewater treatment process of this invention;

FIG. 10 is a schematic block diagram of one embodiment of the biologicalreactor shown in FIG. 9 including an anoxic zone configured to removenitrogen and an anaerobic zone configured to remove phosphorus;

FIG. 11 is a schematic side-view of another embodiment of the system forenhancing a wastewater treatment process of this invention;

FIG. 12 is a schematic side-view of yet another embodiment of the systemfor enhancing a wastewater treatment process of this invention; and

FIG. 13 is a schematic block diagram showing one embodiment of theprimary steps of the method for enhancing a wastewater treatment processof this invention.

DETAILED DESCRIPTION OF THE INVENTION

Aside from the preferred embodiment or embodiments disclosed below, thisinvention is capable of other embodiments and of being practiced orbeing carried out in various ways. Thus, it is to be understood that theinvention is not limited in its application to the details ofconstruction and the arrangements of components set forth in thefollowing description or illustrated in the drawings. If only oneembodiment is described herein, the claims hereof are not to be limitedto that embodiment. Moreover, the claims hereof are not to be readrestrictively unless there is clear and convincing evidence manifestinga certain exclusion, restriction, or disclaimer.

There is shown in FIG. 1 one embodiment of system 10 for enhancing awastewater treatment process of this invention. System 10 may be used toenhance wastewater treatment processes, including, inter alia, activatedsludge wastewater treatment processes, SBR processes, anaerobictreatment reactor processes, or any other similar type wastewatertreatment processes. When used to enhance an activated sludge wastewatertreatment process or an SBR process, system 10 includes at least onebiological reactor 12, e.g., an aeration tank, which receives a flow ofwastewater 14 by line 16. Biological reactor 12 preferably introducesdissolved oxygen 18 by line 20 exposed to ambient air 22 to a populationof microorganisms to promote growth of biological flocs 23 in mixedliquor 24. Mixed liquor 24 is typically a combination of wastewater 14and biological flocs 23 and may be defined by a concentration of mixedliquor suspended solids (MLSS). In other examples, system 10 may also beused to enhance an anaerobic treatment process. In this case, biologicalreactor 12 is configured as an anaerobic treatment reactor. To do this,no oxygen is introduced to reactor 12 and an anaerobic environment iscreated therein.

System 10 also includes weighting agent impregnation subsystem 26 which,in one embodiment, preferably includes weighting agent storage tank 34coupled to line 36, weighting agent impregnation tank 28, and mixer 30.Weighting agent impregnation tank 28 receives mixed liquor 24 frombiological reactor 12 by line 32 or settled sludge from the bottom ofbiological reactor 12 via line 77. Impregnation tank 28 preferablyreceives virgin weighting agent 33, e.g., from weighting agent storagetank 34 by line 36, as shown at 35, and/or recycled weighting agent 38from weight agent recovery subsystem 74.

In one design, weighting agent impregnation subsystem 26 preferablyincludes weighting agent feeder subsystem 110 configured to control thedelivery rate of virgin weighting agent 33 to weighting agentimpregnation tank 28. Weighting agent feeder subsystem 110, FIG. 2,typically includes pneumatic feeder subsystem 112 which includes porousmedia 114, e.g., a plurality of stainless steel screens disposed onselected areas of the inside of weighting agent storage tank 34, e.g.,areas 116 and 118 at the bottom of weighting agent storage tank 34.Porous media 114 is also preferably disposed on the inside of line 36.In one design, pneumatic feeder subsystem 110 is configured to regulatesupply of compressed air 120 by lines 121 to the porous media 114 intank 34 and in line 36 to regulate the delivery rate of weighting agent33 delivered to weighting agent impregnation tank 28. In one example,porous media 114 may be a porous 316 stainless steel material with anultra-smooth finished contact surface made for precise control ofpermeability and strength. Porous media 114 produces an evenlydistributed layer of air 120 that fluidizes weighting agent 33 in areas116 and 118 of storage tank 34 and in line 36 above porous media 114.The boundary layer above porous media 114 reduces buildup, friction, andwear. It also makes weighting agent 33 easier to convey by eliminatingcompaction and drag of weighting agent 33 in areas 116 and 118 ofstorage tank 34 and in line 36. One example of pneumatic feedersubsystem is available from Young Industries (Muncie, Pa.).

In operation, the delivery rate of weighting agent 33 to weighting agentimpregnation tank 28, FIG. 1, is controlled by regulating the amount ofair 120, FIG. 2, delivered by lines 121 to porous media 114. Higherrates of weighting agent 33 delivered to weighting agent impregnationtank 28 may be used for initially impregnating the entire population ofbiological flocs 23 in biological reactor 12 and a secondary clarifier(discussed below) with weighting agent. Thereafter, a maintenance doseof weighting agent 33 may be supplied to weighting agent impregnationtank 28 to maintain a desired concentration of weighting agent.

Mixer 30 mixes the mixed liquor or the settled sludge in tank 28 withvirgin weighting agent 33 and/or the recycled weighting agent 38 toimpregnate the weighting agent into the biological flocs in mixed liquoror the settled sludge to form weighted biological flocs. Mixer 30preferably utilizes a mixing energy sufficient to impregnate theweighting agent into biological flocs suspended in a mixed liquor or thesettled sludge to form weighted biological flocs. The weightedbiological flocs in tank 28 are then sent back to biological reactor 12by line 37. The treated secondary effluent 50 exits reactor 12 by line51.

FIG. 3 shows a microscopic view of one example of biological flocs 23impregnated with virgin weighting agent 33 and recycled weighting agent38 to form weighted biological floc 25.

Because weighted biological flocs generated by weighting agentimpregnation subsystem 26 have a greater specific gravity thannon-impregnated biological flocs, they settle faster thannon-impregnated biological flocs. Thus, the time needed to separateweighted biological flocs from the mixed liquor of system 10 is reducedwhen compared to a conventional activated sludge wastewater treatmentsystem or SBR system. The weighted sludge blanket of an anaerobictreatment system is also more compact and dense and therefore can handlehigher flow rates and is not as diffuse. The result is system 10 cansubstantially increase the capacity of such wastewater systems whileproviding a high quality treated effluent.

In another embodiment, weighting agent impregnation subsystem 26′, FIG.4, where like parts have been given like numbers, may be configured asventuri mixer/eductor 27 having nozzle 31 and funnel 45 which receivesvirgin weighting agent 33, e.g., from tank 34 by line 36, and/orrecycled weighting agent 38 from separator 78. Weighting agentimpregnation subsystem 26′ may also include pneumatic feeder subsystem110, similar as discussed above with reference to FIG. 2 for controllingthe delivery rate of weighting agent 33 to funnel 45, FIG. 4. Venturimixer/eductor 27 preferably receives mixed liquor by line 32 or settledsludge by line 77, as shown in FIG. 1.

In operation, the velocity of mixed liquor in line 32 or the settledsludge in line 77 is increased through nozzle 31. Virgin weighting agent33 and/or recycled weighting agent 38 in funnel 45 enters nozzle 31 byline 39 and travels downstream to line 37. The widening of line 37 at 41induces intimate mixing and entrainment, as shown at 43. Thisimpregnates the virgin and/or recycled weighting agent into thebiological flocs to form weighted biological flocs. The weightedbiological flocs are then returned to biological reactor 12 by line 37,as shown in FIG.

In one example, the weighting agent may be magnetite, or any similartype weighting agent or magnetically separable inorganic material knownto those skilled in the art which increases the density of thebiological flocs when impregnated therein. In one example, the majorityof the weighting agent has a particle size less than about 100 μm. Inother examples, the majority of the weighting agent particles have asize less than about 40 μm or less than about 20 μm.

System 10, FIG. 1, also includes weighting agent recovery subsystem 74which receives settled sludge from biological reactor 12 by line 76.Weighting agent recovery subsystem 74 preferably includes separatorsubsystem 78 which recovers the weighting agent from the weightedbiological flocs in the settled sludge in line 76 and reintroduces(recycles) weighting agent 38 to weighting agent impregnation subsystem26, 26′, FIGS. 1 and 4.

In one design, separator subsystem 78 may be configured as shear mill112, FIG. 5A, which shears the sludge in line 76 to separate theweighting agent from the weighted biological flocs. Shear mill 112ideally includes rotor 80 and stator 82. In operation, the settledsludge in line 76 enters shear mill 112 and flows in the direction ofarrows 180 and enters rotor 80 and then stator 82. Shear mill 112 isdesigned such that there is a close tolerance between rotor 80, FIG. 5Band stator 82, as shown at 83. Rotor 80 is preferably driven at highspeeds, e.g., greater than about 1,000 r.p.m. to form a mixture ofweighting agent and obliterated flocs in area 182, FIG. 5A, of shearmill 112. The mixture of weighting agent and obliterated flocs exitsshear mill 112 by line 79, as shown by arrows 184. FIG. 5C shows infurther detail the structure of one embodiment of shear mill 112.Preferably, rotor 80, FIGS. 5A-5C, and/or stator 82 includes slots whichfunction as a centrifugal pump to draw the settled sludge from above andbelow rotor 80 and stator 82, as shown by paths 182, 183, FIG. 5A, andthen hurl the materials off the slot tips at a very high speed to breakthe weighted biological flocs into the mixture of weighting agent andobliterated flocs. For example, rotor 80, FIG. 5B, may include slots 186and stator 82 may include slots 188. Slots 186 in rotor 80 and/or slots188 in stator 82 are preferably optimized to increase shear energy toefficiently separate the weighting agent from the weighted biologicalflocs. The shear developed by rotor 80 and stator 82 depends on thewidth of slots 186 and 188, the tolerance between rotor 80 and stator82, and the rotor tip speed. In one example, rotor 80 is driven at about9,000 ft/min. The result is shear mill 112 provides a shearing effectwhich effectively and efficiently separates the weighting agent from theweighted biological flocs to facilitate recovery of the weighting agent.

In another design, separator subsystem 78, FIG. 6, where like parts havebeen given like numbers, may be configured as ultrasonic separator 116.Ultrasonic separator 116 typically includes one or more ultrasonictransducers, e.g., ultrasonic transducer 262, 264, 266, 268, and/or 270,available from Hielscher Ultrasonics GmbH, Stuttgart, Germany, whichgenerates fluctuations of pressure and cavitation in the settled sludgein line 76. This results in microturbulences that produce a shearingeffect to create a mixture of weighting agent and obliterated flocs toeffectively separate the weighting agent from the weighted biologicalflocs in the settled sludge. The resulting mixture of weighting agentand obliterated flocs exits ultrasonic separator 116 by line 79.

In yet another design, separator subsystem 78, FIG. 7, where like partshave been given like numbers, may be configured as centrifugal separator118. Centrifugal separator 114 typically includes cylindrical section302 located at the top of hydrocyclone 300 and conical base 304 locatedbelow section 302. The settled sludge in line 76 is fed tangentiallyinto cylindrical section 302 via port 303. Smaller exit port 306(underflow or reject port) is located at the bottom of conical section304 and larger exit port 308 (overflow or accept port) is located at thetop of cylindrical section 302.

In operation, the centrifugal force created by the tangential feed ofthe sludge by port 303 causes the denser weighting agent to be separatedfrom the weighted biological flocs in the settled sludge. The separatedweighting agent is expelled against wall 308 of conical section 304 andexits at port 306. This effectively separates the weighting agent fromthe weighted biological flocs. The recovered weighting agent 38 exitsvia port 306 and may be deposited to weighting agent impregnation system26, 26′, FIGS. 1 and 4. The less dense biological flocs remain in thesludge and exit via port 308 through tube 310 extending slightly intothe body of the center of centrifugal separator 118.

Although as discussed above, separator subsystem 78 may be configured asa shear mill, an ultrasonic separator, or a centrifugal separator, thisis not a necessary limitation of this invention. In other designs,separator subsystem 78 may be configured as a tubular bowl, a chamberbowl, an imperforate basket, a disk stack separator, and the like, asknown by those skilled in the art.

In the example above where a separator 78, FIGS. 5A-5C, is configured asshear mill 112 to create the mixture of weighting agent and obliteratedbiological flocs, wet drum magnetic separator 81, FIG. 8, or centrifugalseparator 118, FIG. 7, may be used to recover the weighting agenttherefrom. Further details of the design and operation of wet drummagnetic separator 81 are disclosed in co-pending application U.S.Publication No. 2008/0164184, entitled “Fluidic Sealing System For a WetDrum Magnetic Separator”, and U.S. Publication No. 2008/016483, entitled“Collection System for a Rotating Wet Drum Magnetic Separator”, bothincorporated by reference herein.

In the example where separator subsystem 78, FIG. 6, is configured as anultrasonic separator 116 to create the mixture of weighting agent andobliterated biological flocs, wet drum magnetic separator 81, FIG. 8, orcentrifugal separator 118, FIG. 7, may be used to recover the weightingagent therefrom.

The result of recovering and recycling the weighting agent as discussedabove with reference to FIGS. 5A-7 significantly reduces the operatingcosts of wastewater treatment system 10.

System 10, FIG. 1 may also include wasting subsystem 83 which wastes theremaining settled sludge of separator subsystem 78 to control thepopulation of the microorganisms in mixed liquor 24 in biologicalreactor 12.

In another embodiment, system 10′, FIG. 9, where like parts have beengiven like numbers includes biological reactor 12, weightingimpregnation subsystem 26 and/or weighting impregnation subsystem 26′,FIG. 4, and weighting agent recovery subsystem 74 with separatorsubsystem 78, which function similar as discussed above with referenceto FIGS. 1-8. In this example, system 10′ also includes flocculantinjection subsystem 42, typically located downstream from biologicalreactor 12, although flocculant injection subsystem 42 may be at anydesired location in system 10. In this example, flocculant injectionsubsystem introduces flocculant 44 into mixed liquor 24 by line 135.Flocculant 44 enhances settling and thickening of the weightedbiological flocs suspended in mixed liquor 24 in secondary clarifier 46and establishes agglomeration of non-impregnated biological flocs and/orpartially impregnated biological flocs with the weighted biologicalflocs in secondary clarifier 46. In one example, flocculant 44 may becationic or anionic polymer, such as Drewfloc® 2270 (Ashland Chemical,New Jersey), or any similar type polymer known to those skilled in theart.

The agglomeration of non-impregnated biological flocs and/or partiallyimpregnated flocs with the weighted biological flocs makes largerweighted biological flocs to provide for rapid settling of the weightedbiological flocs in settling zone 64 of clarifier 46. Flocculant 44 alsoenhances settling and thickening of the weighted biological flocs inthickening zone 66 of clarifier 46 by reducing the size of, andincreasing the density of, the weighted biological flocs. This creates“drainage” channels between the weighted biological flocs which allowwater at bottom 69 of clarifier 46 to flow towards top 71 of clarifier46 and weighted biological flocs to flow towards bottom 69 in thickeningzone 66 of secondary clarifier 46 to enhance the thickening process.

System 10′ also preferably includes secondary clarifier 46 which may beused to separate and collect the weighted biological flocs from themixed liquor. In one example, a rake or siphon (draft tube) subsystem 67is used to remove settled sludge 54 at bottom 69 of clarifier 46.Because the weighted biological flocs have a greater specific gravitythan non-impregnated biological flocs, they settle faster in secondaryclarifier 46 than non-impregnated biological flocs utilized in a typicalsystem for an activated sludge process. Thus, secondary clarifier 46effectively and efficiently separates the weighted biological flocs fromthe mixed liquor to provide secondary effluent 50′. As a result, thetime needed to separate weighted biological flocs from mixed liquor 24of the system 10′ is reduced when compared to a typical activated sludgeor similar type wastewater treatment process. This increases thecapacity of system 10′ to process wastewater 14. Therefore, system 10′is more effective, efficient, reliable, cost effective, and robust thana typical system for an activated sludge process. Moreover, the size ofclarifier 46 and/or biological reactor 12 can be reduced, allowingsystem 10′ to treat the same quantity of wastewater in a smallerfootprint. This reduces the installation costs and land requirements ofsystem 10′. Additionally, the problems associated with the separationprocess of the biological flocs from the mixed liquor in the secondaryclarifier, as discussed in the Background Section, are alleviated.

System 10′, FIG. 9, may also include return activated sludge subsystem70 which recycles the majority of settled sludge 54 in secondaryclarifier 42 to biological reactor 12 by line 72 using pump 47 and/orsends the settled sludge 54 to weighting impregnation subsystem 26, 26′via line 119.

The capacity of system 10′, FIGS. 1-9, to process wastewater 14 may beincreased by increasing the concentration of the MLSS in biologicalreactor 12 by reducing the amount of settled sludge wasted by wastingsubsystem 83. The amount of settled sludge wasted by wasting subsystem83 may also be reduced to increase the concentration of MLSS in aerationtank 12 to enhance nitrification of ammonia in mixed liquor 24. Thenitrification process may also be further enhanced by increasing theamount of dissolved oxygen 18 introduced to biological reactor 12 byline 20.

Coagulant 88, FIGS. 1 and 9, may be added to biological reactor 12, asshown at 90 or to weighting agent impregnation tank 28, as shown at 94,for removing phosphorus and other contaminants from mixed liquor 24 byprecipitation and/or coagulation, as known by those skilled in the art.In other examples, coagulant 88 may be added to flocculant injectionport 42, FIG. 9, as shown at 92, to remove phosphorus by precipitationand/or coagulation. In yet another example, coagulant 88 may be added toweighting agent impregnation tank 28, FIGS. 1 and 9, as shown at 94, orto venture mixer/eductor 27, FIG. 4, as shown at 103, for removingphosphorus by precipitation and/or coagulation.

The ratio of the weighting agent, e.g., magnetite or similar typematerials known to those skilled in the art, to mixed liquor and/orsettled sludge may be greater than about 1.5 to 1.0. In one example,secondary effluent 50 has a suspended solid concentration of less thanabout 30 mg/L, which may meet local, state, and federal guidelines forsecondary effluent 50.

System 10″, FIG. 10, where like parts have been given like numbers, mayinclude biological reactor 12′, e.g., an aeration tank, having anoxiczone 87 with mixer 91 configured to remove nitrogen from mixed liquor24. In this example, recycle line 100 connected to line 135 recyclesmixed liquor 24 to anoxic zone 87, as shown by arrows 101. Biologicalreactor 12′ may also include anaerobic zone 93 with mixer 95 configuredto remove phosphorus from the mixed liquor 24 In this example, line 72of return activated sludge subsystem 70 recycles the settled sludge toanaerobic zone 84. Many other possible biological nutrient removalconfigurations may be utilized, as known to those skilled in the art.

Although as shown above with reference to FIGS. 1 and 9, system 10,includes weighting agent impregnation subsystem 26, 26′ which receivesmixed liquor from biological reactor 12 and then dispenses the weightedbiological flocs back into the biological reactor, this is not anecessary limitation of this invention. In other designs, weightingagent impregnation subsystem 26, 26′, may receive mixed liquor frombiological reactor 12 and dispense the weighted biological flocs betweenbiological reactor and the secondary clarifier. For example, system10′″, FIG. 11, where like parts have been given like numbers, mayinclude weighting impregnation subsystem 26, 26′, similar as discussedabove with reference to FIGS. 1 and 4, which dispenses the weightedbiological flocs to line 137 between biological reactor 12 and clarifier46.

In other designs, weighting agent impregnation subsystem 26, 26′ may belocated between the biological reactor and the secondary clarifier. Forexample, system 10.sup.IV, FIG. 12, where like parts have been givenlike numbers, includes weighting agent impregnation subsystem 26, 26′located between biological reactor 12 and clarifier 46. In this example,wastewater 14 may be from a brewery processing system or similar typeprocessing system which has a high concentration of biodegradableorganic matter in the incoming wastewater 14. In this design, system10.sup.IV may not need return activated sludge subsystem 70, a shown inFIG. 9, because enough organisms are grown from the removal of influentorganic matter to maintain a suitable population of microorganisms inthe mixed liquor 24.

The method for enhancing a wastewater treatment process, in oneembodiment of this invention, includes receiving a flow of wastewater inat last one biological reactor, step 200, FIG. 13. Biological flocs arethen formed in the biological reactor, step 202. Weighting agent is thenimpregnated into the biological flocs to form weighted biological flocs,step 204. The weighting agent is then recovered and reintroduced to step204, step 206. The details of the operation of steps 200-206 arediscussed in detail above with reference to FIGS. 1-9.

Although specific features of the invention are shown in some drawingsand not in others, this is for convenience only as each feature may becombined with any or all of the other features in accordance with theinvention. The words “including”, “comprising”, “having”, and “with” asused herein are to be interpreted broadly and comprehensively and arenot limited to any physical interconnection. Moreover, any embodimentsdisclosed in the subject application are not to be taken as the onlypossible embodiments. Other embodiments will occur to those skilled inthe art and are within the following claims.

In addition, any amendment presented during the prosecution of thepatent application for this patent is not a disclaimer of any claimelement presented in the application as filed: those skilled in the artcannot reasonably be expected to draft a claim that would literallyencompass all possible equivalents, many equivalents will beunforeseeable at the time of the amendment and are beyond a fairinterpretation of what is to be surrendered (if anything), the rationaleunderlying the amendment may bear no more than a tangential relation tomany equivalents, and/or there are many other reasons the applicant cannot be expected to describe certain insubstantial substitutes for anyclaim element amended.

What is claimed is:
 1. A method of treating wastewater comprising:introducing a wastewater into a biological reactor to provide a mixedliquor comprising biological flocs; introducing at least one of themixed liquor and a settled sludge from the biological reactor to aweighting agent impregnation subsystem; contacting a weighting agentwith the at least one of the mixed liquor and the settled sludge in theweighting agent impregnation subsystem to form weighted biologicalflocs; and introducing the weighted biological flocs from the weightingagent impregnation subsystem to the biological reactor.
 2. The method ofclaim 1, further comprising withdrawing an effluent from the biologicalreactor.
 3. The method of claim 1, further comprising introducing theweighted biological flocs from the biological reactor to a separator. 4.The method of claim 3, further comprising separating the weighting agentfrom the weighted biological flocs to provide a refreshed weightingagent and biological flocs.
 5. The method of claim 4, further comprisingcontacting the refreshed weighting agent with the at least one of themixed liquor and the settled sludge in the weighting agent impregnationsubsystem.
 6. The method of claim 4, further comprising removing atleast a portion of the weighted biological flocs from the separator to aprocessing unit.
 7. The method of claim 1, further comprisingintroducing a flocculant to at least one of the wastewater and the mixedliquor.
 8. The method of claim 1, further comprising introducing acoagulant to at least one of the biological reactor, the mixed liquor,and the weighting agent impregnation subsystem.
 9. The method of claim1, further comprising introducing the mixed liquor to a clarifier toprovide a clarified effluent and a settled sludge.
 10. The method ofclaim 9, further comprising withdrawing the clarified effluent from theclarifier.
 11. The method of claim 9, further comprising introducing thesettled sludge from the clarifier to the wastewater.
 12. The method ofclaim 1, further comprising removing nitrogen and phosphorus from themixed liquor.
 13. The method of claim 1, further comprising controllingthe rate of delivery of the weighting agent to the at least one of themixed liquor and the settled sludge in the weighting agent impregnationsubsystem.